efi/cper: Use scnprintf() for avoiding potential buffer overflow

Since snprintf() returns the would-be-output size instead of the
actual output size, the succeeding calls may go beyond the given
buffer limit.  Fix it by replacing with scnprintf().

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200311072145.5001-1-tiwai@suse.de
Link: https://lore.kernel.org/r/20200409130434.6736-2-ardb@kernel.org

diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index b1af0de..9d25129 100644 (file)
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -101,7 +101,7 @@ void cper_print_bits(const char *pfx, unsigned int bits,
                if (!len)
                        len = snprintf(buf, sizeof(buf), "%s%s", pfx, str);
                else
-                       len += snprintf(buf+len, sizeof(buf)-len, ", %s", str);
+                       len += scnprintf(buf+len, sizeof(buf)-len, ", %s", str);
        }
        if (len)
                printk("%s\n", buf);